1. Field of the Invention
The present invention relates to an information processing unit, and in particular, to an information processing unit having an information division recording function capable of preventing unauthorized leakage and unauthorized use of user data stored on the information processing unit such as a PC.
2. Description of the Related Art
When a document is prepared with an information processing unit such as a PC, the document is usually stored as one file on a hard disk or a movable memory medium (e.g., USB memory). However, in a case where the document is stored simply as one file, the content of the file may be subjected to unauthorized use easily if the PC is stolen.
Thus, antitheft measures such as storing the file with encryption or with read restriction requiring a password input have been taken.
In order to further improve the security, a method in which a prepared document is not stored as one file but is divided to be stored separately on two recording media has been adopted.
For example, a prepared document “A” is divided into two files (A1, A2). One file A1 is stored on a hard disk built in the PC, and the other file A2 is stored on a movable USB memory.
When the document A is read, the both files (A1 and A2) are read and constructed into the document A and then displayed or the like. Therefore, the document A cannot be read and edited without the USB memory since the file A2 is missing.
Accordingly, even if only a PC is stolen in a state where the USB memory is removed, the document A in the PC cannot be opened only with the file A1, so it is possible to reduce risks of unauthorized leakage and unauthorized use of data.
Japanese Patent Laid-Open Publication No. 2005-10957 proposes an encryption system using a cache memory, having a cache invalidating function for invalidating old data on the cache memory in accordance with switching between ON and OFF of an encrypting function in order to prevent unencrypted data from remaining on the cache memory.
Also, Japanese Patent Laid-Open Publication No. 2004-240699 proposes a content protection system in which a content is encrypted and written on an HDD, when the content is read, a cache memory is used for temporary storage, and when reading and writing using the cache memory have been completed, the content on the cache memory is completely erased to thereby prevent unauthorized leakage of data.
However, in the conventional method for preventing unauthorized use, a USB memory must be connected to a PC for editing or viewing a prepared file. Therefore, even an authorized user may not be able to edit the file without the USB memory.
Further, the USB memory must be kept connected during editing the file, which might be inconvenient for the user.
Accordingly, when the user leaves only for a while, if the USB memory is kept connected so as not to interrupt the work, the USB memory and the PC are at risk of being stolen together.
That is, even though data is divided and stored, there is a risk of data leakage by theft.
Since the user cannot remove the USB memory at free timing of the user, the same risk is involved if the user forgets to remove the USB memory when leaving.
In order to solve the risk mentioned above even slightly while considering the convenience for the user, it is desired to enable editing even in a state where the USB memory is not connected.
Although there is a case where editing can be continued without a USB memory by storing data on a cache memory as disclosed in Patent Laid-Open Publication No. 2005-10957 and Japanese Patent Laid-Open Publication No. 2004-240699, information on the cache memory is erased completely after a processing such as reading and writing a file has been completed. Therefore, in order to edit the file again, the USB memory must be connected, so this is inconvenient for the user.